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Peterson set an incredible standard this season for NFL players returning from major knee surgery, nearly breaking the NFL single-season rushing record. Griffin need look nowhere else for an inspiration as the Washington Redskins quarterback begins the road back from an operation Wednesday on two ligaments in his right knee.

"I think it gives motivation to everyone," said Russ Paine, a physical therapist in Houston who worked with the Peterson as the Minnesota Vikings running back went through rehab.

Griffin had his lateral collateral ligament repaired and his ACL reconstructed for a second time. The surgery was performed in Florida by orthopedist James Andrews, who was optimistic that Griffin would be back on the field this fall.

"We expect a full recovery, and it is everybody's hope and belief that due to Robert's high motivation, he will be ready for the 2013 season," Andrews said in a statement released by the Redskins. "The goal of his treatment is to give him the best opportunity for a long professional career."

But no two athletes -- or knee surgeries, for that matter -- are exactly alike, so pinning down a date for Griffin's return is an inexact science. Complicating matters is that Griffin tore the ACL in the same knee in 2009 while playing for Baylor.

University of Maryland head team physician Craig Bennett said football players typically need seven to 11 months to return from a second ACL reconstruction, but that it often takes up to a year for the ligament to be fully healed.

"Typically your first season back from an ACL reconstruction, there's a tendency to have some struggles from time to time," Bennett said.

That's what made Peterson so remarkable. He tore an ACL in late December 2011 and was the league's best back in 2012.

Paine said Peterson's focus and intensity in rehab and natural athletic gifts made the quick recovery possible. Many say Griffin has those same qualities, and he was sounding an upbeat tone on Twitter even before the surgery began early Wednesday morning.

"Thank you for your prayers and support. I love God, my family, my team, the fans, & I love this game. See you guys next season," Griffin tweeted.

While Griffin heals, the debate will continue as to whether he should have been on the field when he hurt the knee for a final time in the fourth quarter Sunday's playoff loss to the Seattle Seahawks.

Griffin reinjured his knee in the first quarter and was obviously hobbled, but he stayed in the game after convincing coach Mike Shanahan that all was OK.

"People can limp around; people can be hurting," Hall of Fame quarterback and ESPN analyst Steve Young said Wednesday. "Some of the great John Wayne hero things that have ever happened in football happened because people play hurt."

The first major injury to Griffin's knee was the torn ACL in the third game of the 2009 season with Baylor, when he was hurt on the opening drive against Northwestern State but kept playing until halftime. Griffin missed the rest of the year but returned in 2010 and won the Heisman Trophy in 2011.

Griffin's first notable injury in the pros was a concussion early this season, which led the quarterback to learn to protect his body better while running the ball.

But last month, at the end of a 13-yard scramble, he sprained the LCL when he was hit by Baltimore Ravens defensive tackle Haloti Ngata. Griffin missed one game and returned to play in three more while wearing a bulky knee brace, his mobility clearly hindered.

On Sunday, Griffin hurt the knee again as he fell awkwardly while throwing a pass late in the first quarter against the Seahawks. He was mostly ineffective the rest of the game, completing only four passes after that drive.

Griffin finally departed with 6:19 to play in the game, after the knee buckled while he was trying to field a bad shotgun snap.

The No. 2 overall pick in last year's draft, Griffin was one of several rookie quarterbacks to make an instant impact on the NFL this season. He set the league record for best season passer rating by a rookie QB and led the Redskins to their first NFC East title in 13 years.

Griffin's knee has kept the nation's capital on tenterhooks all week. He was hurt Sunday. Then Shanahan announced Monday that a second opinion was needed.

Then on Tuesday came word that surgery would be taking place. Wednesday was the actual surgery. While it was taking place, District of Columbia Mayor Vincent Gray said he will invite Griffin to watch President Barack Obama's inaugural parade on a reviewing stand outside the district government building later this month.

"I'd love to have him come, but ... he obviously may be unable. His mobility may be impaired somewhat at that point," Gray said. "My focus right now is on having him successfully get through the surgery."